It is well-known that such organic materials as plastics, rubbers, lubricating oils, etc. are prone to oxidation and deterioration in the presence of oxygen. Oxidation of organic materials causes the loss of those intrinsic properties characteristic of the organic material. With a view to preventing deterioration a variety of antioxidants have been developed, however, these antioxidants fail to prevent completely the deterioration of the desired properties of the materials to which they are added. Thus, those skilled in the art are constantly searching for new and more effective antioxidant systems which are useful for the protection of polymers and other organic materials.
Antioxidant synergists have been known in the art for some time. For example U.S. Pat. No. 3,492,336 discloses a novel tetra-alkyl thioethyl thiodisuccinate compound for use with phenolic type antioxidants in the stabilization of polyolefins.
An antioxidant composition comprising a synergistic mixture of a phenol, an amine and a sulfone is described in U.S. Pat. No. 3,839,210. Specifically, U.S. Pat. No. 3,839,210 discloses an antioxidant composition comprised of a mixture of an oil soluble phenol, an oil soluble amine and a long chain alkylthioethyl sulfone compound in an oxidizable organic material, particularly petroleum oils.
In U.S. Pat. No. 3,398,116 a thiocarboxylic acid thioether ester is used in combination with a limited group of phenolic antioxidants to stabilize poly-alpha-olefins against oxidative degradation. It is taught in U.S. Pat. No. 3,398,116 that the antioxidant activity of phenolic antioxidants in poly-alpha-olefin systems rises to an unexpectedly high level when used in association with thiodicarboxylic esters.
A synergistic, terpene-based, antioxidant system is disclosed in U.S. Pat. No. 3,491,044 in which a rosin alcohol ester of thiodipropinonic acid is used in combination with a tris-isobornyl phenol antioxidant to stabilize natural and synthetic polymers, rubber, lubricants and oils, etc.
In addition, U.S. Pat. No. 3,758,549 discloses polyalkanol esters of alkylthio-alkanoic acids as synergists with phenolic antioxidants and U.S. Pat. No. 3,666,716 and U.S. Pat. No. 3,505,225 discloses derivatives of diphenylamine and the phenylnaphthylamines as synergists with dialkyl 3,3'-thiodipropionates.
The art of using a combination of antioxidants has already been put into practice in industry and such antioxidant combinations are often highly effective. There has been prepared a variety of antioxidants which have been examined with a view towards obtaining more stable organic compositions. As a result it has been found that the combined use of the novel compounds of this invention and a phenolic antioxidant brings about an unexpectedly powerful antioxidative effect. None of the above cited patents or other literature in the art has disclosed or even suggests the compounds which are used in the practice of this invention.